Annual and Seasonal Century Scale Trends of the
Precipitation in the Mediterranean Area During the
Twentieth Century
A. Douguedroit and C. Norrant
1 Introduction
A global climate warming between 0.4 and 0.8~C has been assessed during the last
century (IPCC WGI Third Assessment Report, 200 I), but much uncertainty remains
about the evolution of the precipitation during the same period; the mediterranean
case is widely unknown. Here is intended to determine the precipitation centuryscale trends in the Mediterranean area and to search for the representativity of
regional trends versus station ones and of last century trends versus longer ones.
2 Data and Method
The study concerns the Mediterranean area from the Atlantic coast to the Near East
using annual and seasonal data (except summer which is dry in most of the area),
from 1915 to 1988. 41 stations are unequally spread over the area but shorter series
have been added to fill spatial gaps. Mann-Kendall test has been used to check the
homogeneity of the stations.
Rotated Principal Component Analyses (RPCA: Richman 1985), R type, have
been applied with the stations as variables and the precipitation totals of the seasons
or the year as observations. Classes obtained after rotation have been mapped
according to their loadings. They represent the regionalisation of the precipitation
evolution. Their scores have been used as the precipitation history of each region.
Linear trends have been calculated as linear regressions on scores and corresponding
7 years moving averages. The signification of the trends at the 5 % level have been
checked with Spearman -u(r)- and Kendall -u(t)- tests. Trends have also been
calculated and tested for isolated stations and station series longer than a century.
3 Regionalisation of the PreCipitation
According to the seasons, the Mediterranean lands from the Atlantic coast to the
Precipitation in the Mediterranean Area During the
Twentieth Century
A. Douguedroit and C. Norrant
1 Introduction
A global climate warming between 0.4 and 0.8~C has been assessed during the last
century (IPCC WGI Third Assessment Report, 200 I), but much uncertainty remains
about the evolution of the precipitation during the same period; the mediterranean
case is widely unknown. Here is intended to determine the precipitation centuryscale trends in the Mediterranean area and to search for the representativity of
regional trends versus station ones and of last century trends versus longer ones.
2 Data and Method
The study concerns the Mediterranean area from the Atlantic coast to the Near East
using annual and seasonal data (except summer which is dry in most of the area),
from 1915 to 1988. 41 stations are unequally spread over the area but shorter series
have been added to fill spatial gaps. Mann-Kendall test has been used to check the
homogeneity of the stations.
Rotated Principal Component Analyses (RPCA: Richman 1985), R type, have
been applied with the stations as variables and the precipitation totals of the seasons
or the year as observations. Classes obtained after rotation have been mapped
according to their loadings. They represent the regionalisation of the precipitation
evolution. Their scores have been used as the precipitation history of each region.
Linear trends have been calculated as linear regressions on scores and corresponding
7 years moving averages. The signification of the trends at the 5 % level have been
checked with Spearman -u(r)- and Kendall -u(t)- tests. Trends have also been
calculated and tested for isolated stations and station series longer than a century.
3 Regionalisation of the PreCipitation
According to the seasons, the Mediterranean lands from the Atlantic coast to the